The present invention relates to a processing apparatus including a plasma generating means, and particularly to a plasma processing apparatus which is used for plasma etching of a type suitable for forming fine patterns on semiconductor devices or liquid crystal display elements and also suitable for uniformly processing large-diameter substrates, and which is used for plasma CVD and plasma polymerization suitable for forming thin films with fine structures; and the invention relates to a plasma processing method using the plasma processing apparatus.
In a plasma processing apparatus for processing semiconductor elements or liquid crystal display elements using a plasma, it is necessary to control the radical species and the energy of ions to be incident on a substrate to be processed, the directivity of ions, and the uniformity of plasma processing exerting an effect on the processing capability, and also to enhance the productivity of plasma processing.
With respect to the control of radical species, a parallel plate electrode type plasma processing apparatus has been disclosed, for example, in Japanese Patent Laid-open No. Sho 57-131374, and an example of this parallel plate electrode type plasma processing apparatus is shown in FIG. 17.
In the apparatus shown in FIG. 17, a processing chamber 9 surrounded by a cylindrical side wall portion 6, an insulating portion 5, and a disk-like electrode 2 is kept in a vacuum by an evacuating means (not shown). A processing gas is supplied from a gas supplying means 7 into the processing chamber 9 through the electrode 2 serving as a gas introducing passage. In general, the side wall portion 6 is earthed, and is insulated from the electrode 2 by means of the insulating portion 5. The electrode 2 and a stage 3 constitute parallel plate electrodes. When power is applied from a power supply 1 between these parallel plate electrodes, a plasma of the processing gas is generated in the processing chamber 9.
A wafer 4 to be processed is placed on the stage 3 at a lower portion of the processing chamber 9 and is subjected to fine processing by plasma generated in the processing chamber 9 and radical species in the processing gas activated by the plasma. At this time, the plasma density and the temperature of electrons in the plasma are changed, and, at the same time the decomposition state of the processing gas, that is, the amount and the ratio of the radical species exerting an effect on the fine processing capability are changed, depending on the power inputted from the power supply 1, the pressure in the processing chamber 9, the width of the gap between the electrode 2 and the stage 3, and the like.
With respect to control of the energy of the ions, there is a method disclosed in Japanese Patent Laid-open No. Hei 4-239128.
In this method, a divergent magnetic field is provided in such a manner as to be directed perpendicularly to parallel plate electrodes, whereby a self-bias voltage is controlled independently of the output from a high-frequency power supply for generating plasma, so as to independently control the energy of ions to be incident on a substrate by the magnetic field, thereby performing etching at a high accuracy with no damage.
As a method of enhancing the directivity of ions without a reduction in processing rate, there is a method disclosed in Japanese Patent Laid-open No. Hei 8195379.
This method is intended to realize plasma processing capable of generating a high density plasma at a low pressure and of enhancing the controllability of the plasma density distribution by generating a capacitive coupled plasma mixed with an inductive coupled plasma.
As a plasma processing apparatus for controlling the uniformity of plasma processing, there is an apparatus disclosed in Japanese Patent Laid-open No. Sho 61-283127.
In this apparatus, an electrode to which a high-frequency power is applied is divided into a plurality of parts, wherein the power applied to each of the divided electrode parts is independently controlled, to thereby improve the uniformity of plasma processing.
A large problem occurring in the case of enhancing the productivity of plasma processing is that a film, formed on an inner wall surface of a processing chamber during etching or plasma CVD, peels or flakes to give rise to dust, and the dust acts to reduce a rate of production of non-defective products to the total products being produced, such as highly integrated semiconductor devices and liquid crystal display elements, that is, to reduce the production yield. Another problem is that in the course of production, processing characteristics are changed, which also reduces the production yield.
The occurrence of dust will be more fully described below. A deposition film formed on an inner wall surface of a processing chamber by plasma processing is subjected to repeated temperature changes due to variations in heat inputted from the plasma, with a result that a stress occurs in the deposition film. Then, when the film is made thicker, the stress in the film becomes larger than the adhesive force of the film, causing peeling of the film, leading to the occurrence of dust.
A plasma processing apparatus which is intended to remove a deposition film formed on an inner wall surface of a processing chamber is disclosed in Japanese Patent Laid-open No. Hei 8-330282. In this apparatus, the removing rate of a deposition film is enhanced by increasing the energy of ions incident on a surface on which a deposition film is formed.
Further, a method of converting a deposition film formed on an inner wall surface of a processing chamber into a volatile material and exhausting such a material using an evacuating system is disclosed in Japanese Patent Laid-open No. Hei 7-153751. In this method, a non-gaseous material disposed in a processing chamber reacts with the plasma to create reactive chemical species, which in turn react with a deposition film to convert the deposition film into a volatile material, followed by cleaning of the volatile material.
To stabilize the processing characteristics of plasma processing, Japanese Patent Laid-open Nos. Hei 6-188220 and Sho 61-8927 disclose a method of controlling the temperature of an inner wall surface of a plasma processing chamber at a specific value and an apparatus provided with parallel electrodes cooled by a fluid.
With a tendency toward higher integration of semiconductor devices and substrates of larger diameter for producing semiconductor devices, it is further required to attain high selectivity with respect to underlying materials, high accuracies in the processing of shapes, uniform processing of large-sized substrates, and reduction in the occurrence of dust.
1) One factor exerting a large effect on processing characteristics, such as a selectivity, the processing shape and the film quality in plasma etching and plasma CVD, is based on radical species produced by collision of electrons in the plasma. The generation amount and the kinds of radical species are dependent on the energy state of electrons in the plasma.
The energy state of electrons in the plasma is determined on the basis of the collision frequency of electrons depending on the processing pressure, the disappearance rate of electrons due to diffusion of electrons in the plasma, and the like. The energy state of electrons in plasma is expressed by a statistical distribution based on the collision of the electrons with neutral molecules, ions and the like. It has been considered difficult to control such a statistical distribution of the energy state of electrons, except that the statistical distribution can be changed by varying the collision frequency of electrons through control of the processing pressure. For this reason, to control the energy state of electrons, there has been adopted a method of controlling the processing pressure. Such a method of controlling the processing pressure, however, has a problem. That is, in the case of etching, it is difficult to ensure a compatibility between a fine-processing capability and a high selectivity; and, in the case of plasma CVD, it is difficult to ensure a compatibility among the film formation rate, the film quality and the coverage of the device surface.
An object of the present invention is to provide a plasma processing apparatus which is capable of controlling the components and the amount of radical species, not by the conventional manner using process conditions, such as processing pressure, but by providing a means for controlling the energy of electrons in the plasma independently from the plasma generating means and the ion energy controlling means, thereby attaining fine processing with a high selectivity.
2) With respect to the uniformity of plasma processing, it is necessary to ensure a compatibility between control of the radical species, control of the energy of the ions, and the occurrence of a high density plasma at a low pressure.
Further, with a tendency toward larger diameter substrates to be processed, the processing gas flows from a central portion to an outer peripheral portion of a substrate upon etching or plasma CVD. Consequently, both the concentration distribution of the radical species and the thickness distribution of the deposition film come to be actualized. This makes it difficult to uniformly process the entire surface of a large-sized substrate. To solve this problem, it is required to cancel a factor which is impossible in uniform distribution with another control factor relating to the etching characteristics. Such a control factor is required to make it possible to adjust an irregular distribution of plasma for each process condition, independently from other processing conditions, such as the plasma density and the processing pressure.
Another object of the present invention is to provide a plasma processing apparatus having a uniformity controlling mechanism capable of controlling the uniformity of plasma in a state which is compatible with control of the radical species, control of the energy of the ions and the occurrence of a high density plasma at a low pressure, and also which is independent from other processing conditions; and to provide a plasma processing method using the plasma processing apparatus.
3) As described above, to reduce the occurrence of dust, there have been proposed various methods for removing a deposition film which has formed on an inner surface of a processing chamber. Of these methods, however, the method for vaporizing a deposition film and exhausting the vaporized film has a problem in that it takes a lot of time to vaporize the deposition film, resulting in the degraded productivity. Further, a wall surface from which a deposition film is removed is deteriorated because such a wall surface is exposed to radical species and ions in the plasma. As a result, the reaction on the wall surface is changed, to thereby affect the plasma processing characteristics.
Further, an inner wall surface of a processing chamber includes various surface portions which have a different processing state, such as a surface portion to which a high-frequency power is applied and a surface portion which is grounded, and accordingly, reduction in dust must be performed in consideration of these different surface states.
A further object of the present invention is to provide a plasma processing apparatus which is capable of being operated at a specific level of productivity for a long period of time without the occurrence of dust.
To achieve the above object, the present invention provides the following means:
1) A means for generating plasma by capacitive coupled discharge and a means for radiating electromagnetic waves in the plasma are provided, whereby an energy is given from the electromagnetic waves to electrons in the plasma generated by capacitive coupled discharge, to control the energy and the density of electrons, thus adjusting the composition and the amount of radical species.
To be more specific, parallel plate electrodes, an antenna for radiating electromagnetic waves, and a magnetic field allowing the electromagnetic waves radiated by the antenna to pass through the plasma may be provided in a processing chamber, wherein a plasma generating region of the antenna is disposed in such a manner as to be superimposed on a plasma generating region of the parallel plate electrodes, whereby the energy and the density of electrons are controlled by a combination of the plasma generated by the parallel plate electrodes and the plasma due to electromagnetic waves inputted from the antenna.
With this configuration, since the energy of electrons can be controlled by radiation of electromagnetic waves from the antenna, the energy state of electrons in the plasma can be changed by varying the ratio between the power supplied to the parallel plate electrodes for capacitive coupled discharge and the power supplied to the antenna for radiation of electromagnetic waves, to thereby control the amount and the kinds of the radical species.
The intensity of the above magnetic field is also set to be variable with respect to the frequency of electromagnetic waves radiated from the antenna in a range including a value at which electron cyclotron resonance occurs. Accordingly, the energy level given to electrons in plasma can be controlled by varying the intensity of the magnetic field.
2) With respect to control of the uniformity of the plasma, two or more of antennas for radiating electromagnetic waves in the plasma are provided, wherein the plasma distribution is controlled by a means for controlling the electromagnetic waves radiated from each of the antennas.
The fact that the density of electrons can be controlled by radiating electromagnetic waves in the plasma is as described above regarding the radical species generating means.
As an antenna for radiating electromagnetic waves, an electrode for capacitive coupled discharge may be divided into a plurality of parts, and a high-frequency voltage may be generated between each of-adjacent groups of the divided electrode parts to radiate electromagnetic waves between each of the adjacent groups of the divided electrode parts.
By controlling a high-frequency voltage between each of the adjacent groups of the divided electrode parts, it is possible to control the power of the electromagnetic waves radiated between each of the adjacent groups of the divided electrode parts. To control the high-frequency voltage generated between each of the adjacent groups of the divided electrode parts, the phase of a high-frequency voltage applied to each of the divided electrode parts may be controlled.
3) In the case of an electrode to which a high-frequency is applied in a plasma processing chamber, ions are accelerated by a high-frequency electric field and are incident on the electrode. Accordingly, by removing a deposition film adhering on a surface of the electrode through the energy of the ions, dust caused by the deposition film can be reduced.
A surface portion of an electrode may be made from a material which will not react with radical species generated by plasma processing and not produce a nonvolatile material. Further, contact between an electrode and a surface portion of an electrode may be made high to enhance thermal transfer from a surface portion of an electrode to a cooled electrode and to reduce a temperature rise. With this configuration, it is possible to reduce the occurrence of dust due to formation of a non-volatile reaction product on the surface of the electrode, and to stabilize the reaction on the surface of the electrode by reducing the temperature rise and hence to prevent a variation in plasma processing characteristics.
With respect to other portions, the temperature of an inner wall surface of a processing chamber may be kept constant, to prevent the occurrence of stress in a film due to a variation in heat. This prevents occurrence of peeling of the film. Further, by maintaining the temperature on the inner wall surface, the reaction on the surface can be stabilized and thereby a variation in plasma processing characteristics can be prevented.